The present invention relates to an external combustion engine which combines the advantages of a free-piston combustion in which combustion proceeds externally to the motor at very slow rates and of a WANKEL rotary engine in which eccentrically-mounted rotors act as pistons without the assistance of connecting rods, thereby eliminating the alternating motion of massive engine components and ensuing brusquely varying alternatively oriented loads. This enables air cushions to be used between the sliding surfaces of cooperating engine parts.
The motor members of the external combustion engines described in my prior U.S. Patents are also of the rotary type. However, they all use vanes moveable with respect to the rotor. The vanes function so as to form variable-volume confined spaces in which either air compression or gas expansion takes place. The vanes are not positively urged to maintain their geometrical relationships with respect to the two other positively positioned structures which cooperate with the vanes to form such spaces. As a result, the amount of compression and/or expansion that may be obtainable between two contiguous vanes is limited. The number of vanes positionable between the two structures is also necessarily limited for practical reasons. Thus the compression or expansion ratio obtainable per rotor assembly is limited to values that are only a fraction of the compression ratio which an engine must have in order to reach the thermodynamic cycle efficiencies of present piston engines. Such inherent limitations of vane motors force the engine designer to use at least two or preferably three "stages" arranged in series. Ducting of the air and of the combusted gas is thus required between stages.
Because vanes cannot be forcefully radially positioned as the relative rotating motion of the two positively positioned structures takes place, forces must be exerted on the vanes to urge them to seal these intervane spaces. Three types of forces are commonly used, either separately or in conjunction: i.e. centrifugal forces, pressure forces and/or spring forces. Although a vane motor may be designed to operate ideally at a certain rotational speed, using one or more of these forces, it is either difficult or ineffective to make a combination thereof operate equally well at all speeds and/or engine regimes. However, rotary machinery of the type studied and developed by Pr. Felix Wankel (e.g. the Wankel rotary engine) using a single rotor revolving inside an especially spaced containment structure can theoretically provide a mechanically-assured positive positioning of the rotor and insure sealing, without the use of vanes. Thus it appears that combining a Wankel-type of rotary motor with a free-piston combustor may offer promises of simplicity as compared to those obtainable with a rotary vane motor association.
In view of this background, it is an object of the present invention to provide a new and improved combustion engine which combines the most advantageous constructions features of the two types of engines mentioned above but embodied into a simpler engine construction which will operate equally well with various types of fuels reliably and during a longer lifetime.
It is another object of the present invention to provide an improved external combustion engine of simpler construction with fewer simpler mechanical moving parts.
It is another object of the present invention to provide a new and improved engine in which solid friction between moving parts is eliminated, thereby eliminating the need for lubrication and cooling, while minimizing surface wear.
It is another object of the present invention to provide an improved engine in which full expansion of the combusted gases can be achieved, thereby improving the engine thermodynamic cycle efficiency and lowering fuel consumption.
Finally it is still another object of the present invention to provide a new and improved external combustion engine in which heat exchange takes place between the compressed air and the combusted gases, whereby a further increase of thermodynamic cycle efficiency and a further decrease of fuel consumption are obtained, while lower rates of pollutant emission result.